1. Field of the Invention
The present invention relates to an apparatus and a method of estimating road slope of a vehicle. More particularly, the present invention relates to an apparatus and a method of estimating road slope of a vehicle that determines whether the vehicle drives procedure on a chassis dynamometer and estimates road slope by using either a driving torque or the gravitational acceleration sensor depending on the driving state of the vehicle.
2. Description of Related Art
Generally, methods of estimating road slope of a vehicle are classified into a method using a driving torque and a method using a gravitational acceleration sensor.
A load of the vehicle changes depending on road slope, so an increase rate of a vehicle speed regarding the driving torque is changed according to road slope. Thus, the method of estimating road slope by using the driving torque estimates road slope by using a difference of the increase rate of the vehicle speed. The method of estimating road slope by using the driving torque can estimate road slope without an additional sensor. However, the method of estimating road slope by using the driving torque cannot correctly estimate road slope due to change of the driving torque. Thus, an excessive error of road slope occurs due to change of the driving torque.
On the other hand, the method of estimating road slope by using the gravitational acceleration sensor detects a longitudinal acceleration when the vehicle is located on a slope. Thus, the method of estimating road slope by using the gravitational acceleration sensor calculates a pitching slope of the vehicle by comparing the longitudinal acceleration with the increase rate of the vehicle speed. Since the pitching slope is road slope if wheels of the vehicle have a fixed height, the method of estimating road slope by using the gravitational acceleration sensor can estimate road slope regardless of the driving torque.
The method of estimating road slope by using the gravitational acceleration sensor has high accuracy and fast responsiveness compared to the method of estimating road slope by using the driving torque. However, when the vehicle drives procedure on a chassis dynamometer, an output value in a longitudinal direction of the gravitational acceleration sensor because the vehicle does not move and a wheel speed of the vehicle is changed only. Thus, the road slope is estimated incorrectly as a negative value during acceleration and a positive value during deceleration. A shift control of the vehicle is performed according to the road slope. Thus, fuel consumption and power performance of the vehicle cannot be recognized when the road slope is estimated incorrectly during driving procedure on the chassis dynamometer for a fuel consumption certification or a power performance test.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.